This invention relates to a fuel economy running indicator which may be used during the driving operation of an automobile.
In general, an internal combustion engine for a vehicle is designed to have a scope for operating at a constant gear ratio of speed change gears even if the load of the vehicle changes considerably. Accordingly, it is possible that a driver selects the gear ratio within the scope of a certain degree to operate a vehicle, such as a truck, having a number of speed change gears.
However, under a constant power output, the internal combustion engine used for such a vehicle makes it possible to accomplish a satisfactory state of specific fuel consumption, that is, a fuel economy running state, by setting a suitable operation condition and, for this purpose, it is necessary to continually set a suitable gear ratio or proper travel of an accelerator pedal. This has become a substantial problem in this energy conserving age.
Prior to the disclosure of the present invention, the explanation relating to economic fuel consumption will be generally given hereinafter. FIG. 1 shows a general characteristic of a Diesel engine for vehicle wherein a vertical axis T indicates an output torque of the Diesel engine, a horizontal axis N indicates the speed thereof, and loop-like dashed lines e indicate equal fuel consumption curves. The specific fuel consumption increases gradually as the curves go outwardly. A dashed-line characteristic a.sub.1 is at a constant travelling amount of an accelerator pedal and, in response to the travelling amount, is shifted along the vertical axis of FIG. 1, keeping substantially the shape of the characteristic a.sub.1.
In an over-top change gear state (e.g., 6 speed change gears, differential gear ratio x over-top gear ratio=4.25) of a truck mounting the Diesel engine of FIG. 1 and a normal running state under a 100% load and 0% running grade conditions, a running resistance characteristic of the truck is shown as a dashed line i in FIG. 1.
If the truck runs at about 90 Km/h on an express highway, the speed of the Diesel engine comes up to No. If No is constant, it defines a border line c and the output torque T of the engine is given by an operating point f.
When the truck travelling with the running resistance as mentioned above runs on an express highway, as understood from FIG. 1, it is desirable to run at the engine speed approaching to the loop center of the equal fuel consumption curves e as closely as possible and, thus, it is desirable that the truck runs at 80-90 Km/h, that is, the speed thereof is limited below N=No.
In a running state, an automobile must be repeatedly accelerated and decelerated not only in the suburbs but in the town. In the acceleration state, the operating points of the engine exist in the upper area of the running resistance characteristic i.
As described above, in order to minimize the fuel cost in operation in consideration of a high vehicle speed as required on an express highway and a power enough to accelerate the vehicle, it is preferable to operate it within the area defined by border lines a, b and c.
Notably, the border line a indicates an equal travelling amount characteristic of the accelerator pedal which is maintained in the state getting close to the minimum fuel consumption, and this state satisfies a significant increase of the torque T which is required to increase a tractive force of the vehicle.
Also, the border line b means an operating state which is being accelerated from that of the increased tractive force, approaching the minimum fuel consumption as closely as possible, and indicates that, in the engine operation, it is desirable to reduce a travelling amount a.sub.1 of the accelerator pedal, as the engine speed N increases.
Further, the border line c indicates the limited maximum speed of the vehicle and also indicates that it is possible that No gets close to the area of the minimum fuel consumption, if the maximum speed of the vehicle is permitted to be relatively lowered, such as during the running in the town.